1. Field of the Invention
This invention relates to keys having head, shoulder and blade sections with a bit notch pattern formed along one edge of the key blade with at least one longitudinally extending groove formed in the side of a blade.
2. Description of the Prior Art
As illustrated in FIGS. 1A and 2, a typical key for a house lock includes a key blade having a first edge 12 in which is formed a bit notch pattern 14 uniquely configured to match variable length lock tumblers in a typical rotary cylinder lock of the type used for residential lock applications.
FIG. 1A illustrates the cylindrical face 16 of such a lock which includes a lock entrance slot 18 for receiving a key 20. Entrance slot 18 includes opposing sides 22 and 24. Vertically spaced apart first and second opposed key interface ribs 26 and 28 protrude from sides 22 and 24. Entrance slot 18 also includes space apart upper and lower edges 30 and 32. As illustrated in FIG. 1B, the root 40 of the Weslock key rests upon and is vertically indexed by lower edge 32 of lock entrance slot 16, rather than by key reference surface 50.
As illustrated in FIG. 2, key 20 includes a head 34, a shoulder 36 abutting the head and a longitudinally extending blade 38 coupled to shoulder 36 and including a root 40 and a bitted surface with a unique bit notch pattern 14 for actuating the matching lock.
As illustrated in FIG. 1A, key 20 also includes first and second vertically displaced, longitudinally extending grooves formed in opposing sides of the key. First groove 46 includes a key reference surface 50 for engaging a lock reference surface 52.
As illustrated in FIG. 2, master key 20 having an existing bit notch pattern 14 is duplicated by locking it in a first key clamp 54 of a conventional prior art root-referenced key duplication machine. Key root 40 of master key 20 is placed in abutting contact with a key alignment surface of clamp 54 while geometrically identical key blank 56 is secured in key clamp 58 with its key root 40 aligned to coincide with the alignment of key root 40 of master key 20.
The bit notch pattern 14 of master key 20 is then duplicated on edge 12 of key blank 56 by laterally displacing the key tracing guide 60 along the bit notch pattern 14 of master key 20. Because the rotary cutting wheel 62 is coupled to tracing guide 60 to accurately reproduce both lateral and vertical displacements of the tracing guide as it follows the bit notch pattern of master key 20, cutting wheel 62 accurately reproduces the bit notch pattern of master key 20 into the blade of key blank 56.
In accomplishing the key duplication process described above, prior art root-referenced key duplicating machines measure and reproduce a varying magnitude reference distance 64 defined by the spacing at given lateral positions along the key blade between key root 40 and the bit notch pattern 14. Because according to prior art practice key blank 56 must be geometrically identical to master key 20, cutting wheel 62 accurately reproduces the master key reference distance 64 as a function of lateral position and thereby accurately duplicates the bit notch pattern of master key 20 onto key blank 56.
A primary problem with such prior art key duplication systems is that a key duplication business must maintain an exceedingly large inventory of key blanks geometrically identical to the master keys used by each different brand of house locks to produce operable root-referenced copies of a master key. For house keys, the most popular keys and locks are manufactured by nine different companies and the geometry of each of these nine different keys differs for each different manufacturer. To duplicate house keys, a locksmith must maintain an inventory of nine different house key blanks to properly serve the public.
As illustrated in FIG. 3, in some instances, a key blank geometrically dissimilar to a master key for a different lock brand can be physically inserted into the lock entrance slot of a lock for which it was not intended. FIG. 3 illustrates the problems which arise when a key duplicator uses the prior art root-referenced key duplication system described in connection with FIG. 2 to duplicate a master key onto a geometrically dissimilar key blank.
In FIG. 3, reference lines 66 and 68 are equal in length and indicate that a root-referenced key duplicator has accurately reproduced the root to bit notch distance of the master key onto the dissimilar key blank. Because the spacing between key root 40 and key reference surface 50 of the master key is significantly greater than the distance between key root 40 and key reference surface 50 of the dissimilar key blank, the vertical elevation of the bit notch depth of the dissimilar key (designated by reference number 70) will be displaced substantially above the corresponding bit notch depth elevation of the master key (designated by reference number 72). Accordingly, although the dissimilar key blank may include a bit notch pattern identical to the bit notch pattern of the master key, the dissimilar key blank will not actuate the lock matching the master key bit notch pattern.
Prior art root-referenced key duplication devices therefore typically duplicate house keys by using key blanks geometrically identical to each of the nine different types of commonly used master keys.
U.S. Pat. No. 3,841,175 (Comtois) discloses a method for cutting off the root of previously duplicated house keys to prevent their further duplication on root-referenced key duplication machines. According to the teachings of this patent, a house key is first duplicated onto a geometrically identical key blank. The duplicated key is then further machined to remove the root surface from the key destroying the ability of a root-referenced key duplication machine to accurately reproduce the root to bit notch pattern geometry of the original key. As a result, the rootless duplicate key represents a relatively secure key which cannot be duplicated using ordinary root-referenced key duplication techniques.